Golf ball incorporating an innermost hollow portion

ABSTRACT

Golf ball incorporating: spherical or aspherical innermost hollow portion; shell layer, one or more outer core layers, and at least one cover layer. Shell layer has outer surface hardness greater than inner surface hardness by up to about 7 Shore C to define first hardness gradient. Outer core layer has a second hardness gradient. A shell layer surrounding a spherical hollow portion may have an inner surface with a non-uniform contour defining a phantom spherical circumference of the innermost spherical hollow portion at symmetrically spaced locations about the golf ball&#39;s geometric center. In golf balls including a spherical or aspherical innermost hollow portions, the outer surface can have non-uniform contour bordering and defining a contour of a second inner surface of outer core layer. The outer surface hardness and a second inner surface hardness of second inner surface differ and alternate symmetrically and circumferentially about the shell layer inner surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patent application Ser. No. 14/959,190, filed on Dec. 4, 2015, and also a continuation-in-part of U.S. patent application Ser. Nos. 13/736,993, 13/736,997, 13/737,026, and 13/737,041, each filed on Jan. 9, 2013, the entire disclosures of which are hereby incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This invention relates generally to hollow core golf ball constructions that target desirable aerodynamic and/or inertial properties and feel without sacrificing durability.

BACKGROUND OF THE INVENTION

In recent years, virtually all golf balls are of a solid construction, typically including a solid core encased by a cover, both of which can have multiple layers, such as a dual core having a solid center and an outer core layer, or a multi-layer cover having an inner and outer cover layer. Golf ball cores are often formed at least in part from a thermoset rubber composition with polybutadiene as the base rubber. The cores are usually heated and crosslinked to create a core having certain pre-determined characteristics, such as compression or hardness, which result in a golf ball having the properties for a particular group of players, whether it be professionals, low-handicap players, or mid-to-high handicap golfers. From the perspective of a golf ball manufacturer, it is desirable to have cores exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability.

Accordingly, golf ball manufacturers continuously experiment with golf ball constructions and material formulations in order to target and improve aerodynamic and/or inertial properties and achieve desired feel without sacrificing durability. One such novel construction with no past commercial success is a golf ball having a hollow core—meaning the innermost portion of the core is hollow, surrounded by a ‘shell layer’ and one or more core and cover layers. In some hollow core golf ball constructions, an aspherical hollow space has been created using an insert containing hollow spaces.

However, while many prior commercially available golf balls have been constructed with non-solid centers such as liquid centers, very few golf balls having hollow centers have ever been pursued. One reason is that it has been difficult to implement hollow cores in golf ball constructions and target/improve aerodynamic and/or inertial properties and achieve desired feel without sacrificing durability.

Related co-owned U.S. application Ser. No. 14/959,190, filed on Dec. 4, 2015 (“'190 application) addresses such adhesion issues. In particular, the '190 application discloses golf balls wherein an aspherical hollow space can be created within the core without using an insert, which prior golf balls had incorporated to create the aspherical hollow center. One problem encountered with the prior golf balls incorporating inserts to create an aspherical hollow space within the core was that poor bonding/adhesion sometimes occurred between the insert and an adjacent surrounding layer, resulting in separation of outer layer from the insert when the golf ball was struck by a club face. In golf balls of the '190 application, a plurality of extensions of the shell layer advantageously border and define the aspherical shape of the hollow space within the core. Accordingly, any adhesion problems previously encountered between the insert and outer layer are totally eliminated.

However, there still remains a need for versatile and cost effective hollow core golf ball constructions that can be implemented in spherical and aspherical hollow core designs alike to produce excellent adhesion therein. Such constructions, which meanwhile target desired playing characteristics and feel with excellent continuity of hardness distribution from the hollow interior radially outward, would be particularly desirable. The golf balls of the invention address and solve all of these needs.

SUMMARY OF THE INVENTION

Accordingly, a golf ball of the invention incorporates a hollow innermost portion that may be spherical or aspherical, and displays excellent adhesion between layers with desirable continuity of hardness distribution from the innermost hollow portion outward toward the golf ball outermost surface. Advantageously, the core of a golf ball of the invention incorporates a shell layer having a non-uniform thickness, and a first hardness gradient that extends from an inner surface of the shell layer to an outer surface thereof. In particular, the inner surface has an inner surface hardness, and the outer surface has an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define the first hardness gradient.

In one embodiment wherein the innermost hollow portion is spherical, the inner surface of the shell layer may in particular have a non-uniform contour that defines a phantom spherical circumference of the innermost spherical hollow portion at symmetrically spaced locations about the golf ball's geometric center. In this embodiment, a plurality of hollow spaces is thereby created adjacent to the phantom circumference wherein the hollow spaces and the shell layer alternate symmetrically and circumferentially about the innermost spherical hollow portion. In this construction, the area immediately adjacent the innermost spherical hollow portion therefore comprises alternating hardnesses of the inner surface and the hollow spaces, thereby providing excellent continuity of hardness distribution from the innermost spherical hollow portion, which has a zero hardness, and radially outward. Advantageously, the hollow spaces have the same zero hardness as the innermost spherical hollow portion, which creates a gradual transition from the zero hardness of the very center of the golf ball to the greater hardnesses of the inner surface of the shell layer and further outward. Additionally, a second hardness gradient in the outer core layer continues in creating such excellent continuity of hardness distribution and adhesion between golf ball layers in a spherical innermost hollow-type core construction.

In embodiments wherein the innermost hollow portion is spherical or aspherical, the outer surface of the shell layer can have a non-uniform contour that borders and defines a contour of a second inner surface of an outer core layer that is disposed about the outer surface of the shell layer. The outer surface hardness and a second inner surface hardness of the second inner surface differ. In this embodiment, the outer surface hardness and second inner surface hardness may alternate symmetrically and circumferentially about the inner surface of the shell layer. And once again, the outer core layer has a second hardness gradient to further and continue excellent continuity of hardness distribution and adhesion between golf ball layers in golf ball incorporating either spherical or aspherical innermost hollow portion-type core constructions.

For golf balls incorporating a spherical innermost hollow portion, embodiments are therefore envisioned wherein both the inner surface and outer surface of the shell layer simultaneously have non-uniform contours. In such embodiment, the non-uniform contours may mirror each other or differ, as long as each is symmetrically and circumferentially spaced about the golf ball's geometric center so as to achieve uniform fight and roll when the golf ball is struck by a club face.

These and other elements of a golf ball of the invention as set forth below and elsewhere herein meanwhile target desired playing characteristics and feel. In a first embodiment, the golf ball comprises a hollow core comprising an innermost spherical hollow portion having a diameter of about 0.15 inches to about 1.1 inches. A shell layer, surrounding the innermost spherical hollow portion, is formed from a thermoplastic composition and has a non-uniform thickness, with an inner surface having an inner surface hardness, and an outer surface having an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient. The first hardness gradient in one embodiment may alternatively be about 1 to 5 Shore C.

In one embodiment, the inner surface has a non-uniform contour that defines a phantom spherical circumference of the innermost spherical hollow portion at symmetrically spaced locations thereat. In this embodiment, a plurality of hollow spaces are thereby created adjacent to the phantom circumference which alternate with the shell layer symmetrically and circumferentially about the innermost spherical hollow portion such that uniform flight and roll occur when the finished golf ball is struck by a club face.

Meanwhile, at least one outer core layer, formed from a thermoset composition and having a second hardness gradient, is formed about the outer surface of the shell layer. In one embodiment, the second hardness gradient is a negative hardness gradient of about 3 to 25 Shore C. In another embodiment, the second hardness gradient is a positive hardness gradient of about 3 to 25 Shore C.

In one embodiment, the golf ball may further comprise a thermoplastic intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a thermoplastic composition that is different than the thermoplastic composition of the shell layer.

Alternatively, the golf ball may comprise a thermoset intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a thermoset composition that is different than the thermoset composition of the outer core layer; wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C. For example, the thermoset composition of the outer core layer may comprise a thermoset rubber composition whereas the thermoset intermediate core layer comprises a different thermoset composition.

In another embodiment, the outer surface may have a non-uniform contour that borders and defines a contour of a second inner surface of an outer core layer that is disposed about the outer surface of the shell layer. The outer surface hardness and a second inner surface hardness of the second inner surface differ. In this embodiment, the outer surface hardness and second inner surface hardness may alternate symmetrically and circumferentially about the inner surface of the shell layer.

Of course, constructions are envisioned wherein the shell layer includes both of the aforementioned embodiments described above relating to the contour of the inner surface and the contour of the outer surface.

Many suitable patterns and designs are envisioned for the contour in a shell layer having a non-uniform thickness—for example, the shell layer may have an inner and/or outer surface contour that is wave-like.

At least one cover layer is disposed about the at least one outer core layer. In one embodiment, the cover comprises an inner cover layer disposed about the outer core layer and comprising an ionomeric material and having a first hardness; and an outer cover layer disposed about the inner cover layer and comprising a polyurea or a polyurethane and having a second hardness less than the first.

In a second embodiment, the shell layer is formed from a first thermoset rubber composition; and at least one outer core layer is formed from a second thermoset composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient different from the first hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. In another embodiment, the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C. In yet another embodiment, the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C.

The golf ball may further comprise a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer; wherein the inner cover layer has a material hardness greater than about 60 Shore D; and wherein the outer cover layer has a material hardness of less than about 60 Shore D; and wherein the surface hardness is greater than the inner surface hardness by about 10 to 25 Shore C.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer disposed between the shell layer and the outer core layer comprising a third thermoset rubber composition different from the first and the second; wherein the surface hardness is greater than the inner surface hardness by about 10 to 25 Shore C.

In a third embodiment, the shell layer is formed from a thermoset rubber composition; and at least one outer core layer is formed from a thermoplastic composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. In another embodiment, the second hardness gradient is a negative hardness gradient of about 1 to 10 Shore C. In yet another embodiment, the second hardness gradient is a positive hardness gradient of about 1 to 10 Shore C.

The golf ball may further comprise a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer comprising a thermoplastic composition that is different than the thermoplastic composition of the outer core layer; wherein the inner cover layer has a material hardness greater than about 60 Shore D; and wherein the outer cover layer has a material hardness of less than about 60 Shore D; and wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer disposed between the shell layer and the outer core layer comprising a thermoset composition that is different than the thermoset rubber composition of the shell layer; wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C.

In a fourth embodiment, the shell layer may be formed from a first thermoplastic composition; and at least one outer core layer formed from a second thermoplastic composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient different from the first hardness gradient.

The golf ball may further comprise a thermoplastic intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a third thermoplastic composition different from the first and the second.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a thermoset composition.

In a fifth embodiment, the shell layer may be formed from a first thermoset composition; and at least one outer core layer formed from a second thermoset composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface has an outer surface hardness greater than the inner surface hardness by about 10 to 25 Shore C to define a first hardness gradient; and the outer core layer has a second hardness gradient different from the first hardness gradient.

In each of these embodiments, the spherical hollow portion may alternatively have a diameter of about 0.20 inches to about 1.1 inches, or of about 0.20 inches to about 0.90 inches, or of about 0.25 inches to about 1.1 inches. And the cover may have one or more layers as defined herein.

Furthermore, the outer surface hardness may in one embodiment be greater than about 55 Shore C.

Moreover, the shell layer may have a coefficient of restitution less than about 0.700 when measured at an incoming velocity of 125 ft/s. And a combination of the shell layer and the outer core layer may have a coefficient of restitution (measured at an incoming velocity of 125 ft/s) that is higher than the coefficient of restitution (also measured at an incoming velocity of 125 ft/s) of the shell layer by 10-50%.

In one embodiment, the inner cover has a hardness of greater than about 60 Shore D and the outer cover layer has a hardness of less than about 60 Shore D. And the golf ball may have a first volume, and the spherical hollow portion have a second volume that is about 2% to 30% of the first volume.

Advantageously, a golf ball of the invention may also be constructed to target desired playing characteristics and feel yet create excellent adhesion between layers and continuity of hardness distribution in aspherical hollow core golf balls.

In a first embodiment, the golf ball comprises a core, and one or more cover layers. The core comprises an innermost aspherical hollow portion, a shell layer, and one or more outer core layers. The innermost aspherical hollow portion has a volume V_(ahp). The shell layer is formed from a thermoplastic composition and has an inner surface comprising a plurality of symmetrically spaced extensions that border and define a shape of the innermost aspherical hollow portion. The plurality of extensions and innermost aspherical hollow portion, combined, form a phantom sphere having a diameter of from about 0.15 inches to about 1.1 inches. And the plurality of extensions have a combined total volume E_(TV) such that V_(ahp)≧E_(TV)>0.20 (E_(TV)+V_(ahp)).

Meanwhile, the shell layer also has a non-uniform contour that borders and defines a contour of a second inner surface of an outer core layer that is disposed about the outer surface of the shell layer. The outer surface hardness and a second inner surface hardness of the second inner surface differ. In this embodiment, the outer surface hardness and second inner surface hardness may alternate symmetrically and circumferentially about the inner surface of the shell layer as well as about the golf ball's geometric center.

Additionally, the inner surface has an inner surface hardness and the outer surface has an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient; and the outer core layer has a second hardness gradient.

The aspherical hollow portion has a shape that is axially symmetric. The aspherical hollow portion may be at least one of non-spherical or irregularly-shaped.

The plurality of extensions and innermost aspherical hollow portion, combined, may alternatively form a spherical phantom sphere having a diameter of from about 0.30 inches to about 0.90 inches.

In one embodiment, the outer core layer is formed from a thermoset composition. In another embodiment, the at least one outer core layer is formed from a thermoplastic composition.

The first hardness gradient may alternatively be about 1 to 5 Shore C.

The innermost aspherical hollow portion, shell layer and outer core layer, combined, may have an outer diameter of from about 0.75 inches to about 1.62 inches, for example. The second hardness gradient may be a negative hardness gradient of about 3 to 25 Shore C. Alternatively, the second hardness gradient may be a positive hardness gradient of about 3 to 25 Shore C.

That is, the plurality of extensions have a combined volume E_(TV) that is equal to or less than volume V_(ahp) of the innermost aspherical hollow portion but greater than 20% of the total volume E_(TV)+V_(ahp) of the plurality of extensions and innermost aspherical hollow portion, combined.

Herein, the phantom sphere has a volume that is defined by the maximum radial distance of the innermost aspherical hollow portion. In golf balls of the invention, the shell layer may have a maximum thickness, including extensions, of up to about 0.40 inches, as long as the combined volume E_(TV) of the extensions is such that V_(ahp)≧E_(TV)>0.20(E_(TV)+V_(ahp)). In an alternative embodiment, the combined volume E_(TV) of the extensions is such that V_(ahp)≧E_(TV)>0.30(E_(TV)+V_(ahp)).

And the shell layer thickness at locations not containing extensions may in some embodiments be at least partially less than the maximum thickness, with the extensions being sized and shaped such that their combined volume E_(TV) satisfy the relationship V_(ahp)≧E_(TV)>0.20(E_(TV)+V_(ahp)). In other embodiments, the shell layer thickness at locations not containing extensions may be at least partially equal to the maximum thickness. Regardless, the shell layer has a substantially non-uniform thickness even at locations not containing extensions, due to the contour of the shell layer outer surface.

In one embodiment, the at least one cover layer comprises an inner cover layer disposed about the outer core layer, and an outer cover layer disposed about the inner cover layer, wherein the inner cover layer comprises an ionomeric material and has a first hardness and the outer cover layer comprises a polyurea or a polyurethane and has a second hardness less than the first.

In a second embodiment, the shell layer is formed from a first thermoset rubber composition; and at least one outer core layer is formed from a second thermoset composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient different from the first hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. In another embodiment, the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C. In yet another embodiment, the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C.

The golf ball may further comprise a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer; wherein the inner cover layer has a material hardness greater than about 60 Shore D; and wherein the outer cover layer has a material hardness of less than about 60 Shore D; and wherein the surface hardness is greater than the inner surface hardness by about 10 to 25 Shore C.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer disposed between the shell layer and the outer core layer comprising a third thermoset rubber composition different from the first and the second; wherein the surface hardness is greater than the inner surface hardness by about 10 to 25 Shore C.

In a third embodiment, the shell layer is formed from a thermoset rubber composition; and at least one outer core layer is formed from a thermoplastic composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. In another embodiment, the second hardness gradient is a negative hardness gradient of about 1 to 10 Shore C. In yet another embodiment, the second hardness gradient is a positive hardness gradient of about 1 to 10 Shore C.

The golf ball may further comprise a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer comprising a thermoplastic composition that is different than the thermoplastic composition of the outer core layer; wherein the inner cover layer has a material hardness greater than about 60 Shore D; and wherein the outer cover layer has a material hardness of less than about 60 Shore D; and wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer disposed between the shell layer and the outer core layer comprising a thermoset composition that is different than the thermoset rubber composition of the shell layer; wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C.

In a fourth embodiment, the shell layer may be formed from a first thermoplastic composition; and at least one outer core layer formed from a second thermoplastic composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient different from the first hardness gradient.

The golf ball may further comprise a thermoplastic intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a third thermoplastic composition different from the first and the second.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a thermoset composition.

In a fifth embodiment, the shell layer may be formed from a first thermoset composition; and at least one outer core layer formed from a second thermoset composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface has an outer surface hardness greater than the inner surface hardness by about 10 to 25 Shore C to define a first hardness gradient; and the outer core layer has a second hardness gradient different from the first hardness gradient.

In each of these embodiments, the spherical hollow portion may alternatively have a diameter of about 0.20 inches to about 1.1 inches, or of about 0.20 inches to about 0.90 inches, or of about 0.25 inches to about 1.1 inches. And the cover may have one or more layers as defined herein.

Furthermore, the outer surface hardness may in one embodiment be greater than about 55 Shore C.

Moreover, the shell layer may have a coefficient of restitution less than about 0.700 when measured at an incoming velocity of 125 ft/s. And a combination of the shell layer and the outer core layer may have a coefficient of restitution (measured at an incoming velocity of 125 ft/s) that is higher than the coefficient of restitution (also measured at an incoming velocity of 125 ft/s) of the shell layer by 10-50%.

A golf ball of the invention may be alternatively constructed to target desired playing characteristics and feel yet create excellent adhesion between layers and continuity of hardness distribution in aspherical hollow center golf balls.

In a different embodiment of a golf ball incorporating an aspherical innermost hollow portion, the golf ball comprises a core and one or more cover layers. The core comprises a shell layer that is formed from a thermoplastic composition and has an inner surface comprising a plurality of symmetrically spaced extensions that border and define a shape of an innermost aspherical hollow portion. The innermost aspherical hollow portion comprises from about 2% to about 30% of a total volume of the golf ball. The shell layer also has a non-uniform contour that borders and defines a contour of a second inner surface of an outer core layer that is disposed about the outer surface of the shell layer. The outer surface hardness and a second inner surface hardness of the second inner surface differ. In this embodiment, the outer surface hardness and second inner surface hardness may alternate symmetrically and circumferentially about the inner surface of the shell layer.

Additionally, the inner surface has an inner surface hardness and the outer surface has an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient; and the outer core layer has a second hardness gradient.

The innermost aspherical hollow portion has a shape that is axially symmetric.

The innermost aspherical hollow portion may be at least one of non-spherical or irregularly-shaped.

The plurality of extensions and innermost aspherical hollow portion, combined, form a phantom sphere having a diameter of from about 0.15 inches to about 1.1 inches.

In one embodiment, the first hardness gradient may be about 1 to 5 Shore C.

The innermost aspherical hollow portion, shell layer and outer core layer, combined, have an outer diameter of from about 0.75 inches to about 1.62 inches.

The second hardness gradient may have a negative hardness gradient of about 3 to 25 Shore C. Alternatively, the second hardness gradient may be a positive hardness gradient of about 3 to 25 Shore C.

In one embodiment, the at least one outer core layer is formed from a thermoset composition. In another embodiment, the at least one outer core layer is formed from a thermoplastic composition.

In one embodiment, the at least one cover layer comprises an inner cover layer disposed about the outer core layer, and an outer cover layer disposed about the inner cover layer, wherein the inner cover layer comprises an ionomeric material and has a first hardness, and the outer cover layer comprises a polyurea or a polyurethane and has a second hardness less than the first.

In a second embodiment, the shell layer is formed from a first thermoset rubber composition; and at least one outer core layer is formed from a second thermoset composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient different from the first hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. In another embodiment, the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C. In yet another embodiment, the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C.

The golf ball may further comprise a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer; wherein the inner cover layer has a material hardness greater than about 60 Shore D; and wherein the outer cover layer has a material hardness of less than about 60 Shore D; and wherein the surface hardness is greater than the inner surface hardness by about 10 to 25 Shore C.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer disposed between the shell layer and the outer core layer comprising a third thermoset rubber composition different from the first and the second; wherein the surface hardness is greater than the inner surface hardness by about 10 to 25 Shore C.

In a third embodiment, the shell layer is formed from a thermoset rubber composition; and at least one outer core layer is formed from a thermoplastic composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. In another embodiment, the second hardness gradient is a negative hardness gradient of about 1 to 10 Shore C. In yet another embodiment, the second hardness gradient is a positive hardness gradient of about 1 to 10 Shore C.

The golf ball may further comprise a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer comprising a thermoplastic composition that is different than the thermoplastic composition of the outer core layer; wherein the inner cover layer has a material hardness greater than about 60 Shore D; and wherein the outer cover layer has a material hardness of less than about 60 Shore D; and wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer disposed between the shell layer and the outer core layer comprising a thermoset composition that is different than the thermoset rubber composition of the shell layer; wherein the surface hardness is greater than the inner surface hardness by about 3 to 25 Shore C.

In a fourth embodiment, the shell layer may be formed from a first thermoplastic composition; and at least one outer core layer formed from a second thermoplastic composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface having an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient. And the outer core layer has a second hardness gradient different from the first hardness gradient.

The golf ball may further comprise a thermoplastic intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a third thermoplastic composition different from the first and the second.

Alternatively, the golf ball may further comprise a thermoset intermediate core layer that is disposed between the shell layer and the outer core layer and comprises a thermoset composition.

In a fifth embodiment, the shell layer may be formed from a first thermoset composition; and at least one outer core layer formed from a second thermoset composition disposed about the shell layer. The shell layer has an inner surface having an inner surface hardness and an outer surface has an outer surface hardness greater than the inner surface hardness by about 10 to 25 Shore C to define a first hardness gradient; and the outer core layer has a second hardness gradient different from the first hardness gradient.

In each of these embodiments, the spherical hollow portion may alternatively have a diameter of about 0.20 inches to about 1.1 inches, or of about 0.20 inches to about 0.90 inches, or of about 0.25 inches to about 1.1 inches. And the cover may have one or more layers as defined herein.

Furthermore, the outer surface hardness may in one embodiment be greater than about 55 Shore C. Moreover, the shell layer may have a coefficient of restitution less than about 0.700 when measured at an incoming velocity of 125 ft/s. And a combination of the shell layer and the outer core layer may have a coefficient of restitution (measured at an incoming velocity of 125 ft/s) that is higher than the coefficient of restitution (also measured at an incoming velocity of 125 ft/s) of the shell layer by 10-50%.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings form a part of the specification and are to be read in conjunction therewith. The illustrated embodiments, however, are merely examples and are not intended to be limiting. Like reference numerals and designations in the various drawings indicate like elements.

FIG. 1 is a golf ball incorporating a shell layer having a non-uniform thickness according to one embodiment of the invention;

FIG. 2 is a golf ball of the invention incorporating a shell layer having a non-uniform thickness according to another embodiment of the invention; and

FIG. 3 is a golf ball of the invention incorporating a shell layer having a non-uniform thickness according to yet another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Golf balls of the present invention may include multi-layer golf balls, such as one having a core and a cover surrounding the core, but are preferably formed from a core having a hollow core and at least one outer core layer, an inner cover layer, and an outer cover layer. Any of the core or cover layers may include more than one layer. The cover layer of the golf ball may be a single layer or formed of a plurality of layers, such as an inner cover layer and an outer cover layer. The hollow core comprises an innermost hollow portion that may be spherical in some embodiments, or aspherical in other embodiments.

Advantageously, a golf ball of the invention incorporates a shell layer having a non-uniform thickness, with an inner surface of the shell layer has an inner surface hardness, and an outer surface has an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient. In a first embodiment, incorporating a spherical innermost hollow portion, the inner surface has a non-uniform contour that defines a phantom spherical circumference of the innermost spherical hollow portion at symmetrically spaced locations thereat. In this embodiment, a plurality of hollow spaces is thereby created adjacent to the phantom circumference wherein the hollow spaces and the shell layer alternate symmetrically and circumferentially about the innermost spherical hollow portion.

In second embodiment, the golf ball may incorporate a spherical or aspherical innermost hollow portion, with the outer surface of the shell layer having a non-uniform contour that borders and defines a contour of a second inner surface of an outer core layer that is disposed about the outer surface of the shell layer. The outer surface hardness and a second inner surface hardness of the second inner surface differ. In this embodiment, the outer surface hardness and second inner surface hardness alternate symmetrically and circumferentially about the inner surface of the shell layer.

Constructions are also envisioned wherein the shell layer incorporates an innermost spherical hollow portion and both the first and second shell layer embodiments.

Meanwhile, the outer core layer has a second hardness gradient.

Many different patterns/designs are envisioned as being suitable for forming shell layer surface contours that can be symmetrically circumferentially disposed about the innermost hollow portion so as to ensure uniform golf ball flight and roll.

The first embodiment arrangement permits multiple hardnesses to occur immediately surrounding the innermost hollow portion, thereby creating excellent continuity of hardness distribution within the hollow center golf ball while meanwhile providing excellent adhesion between the shell layer and surrounding outer core layer in a hollow core golf ball construction. Specifically, the inner surface hardness and a zero hardness of the hollow spaces alternate circumferentially about a zero hardness innermost spherical hollow center.

And the second embodiment golf ball construction permits multiple hardnesses to occur about the interface between the outer surface of the shell layer and the inner surface of the outer core layer and circumferentially about the innermost hollow portion. For additional examples and details suitable for a golf ball of the invention, see for example, related applications U.S. patent application Ser. No. 14/959,190, filed on Dec. 4, 2015, and also a continuation-in-part of U.S. patent application Ser. Nos. 13/736,993, 13/736,997, 13/737,026, and 13/737,041, each filed on Jan. 9, 2013, and incorporated herein by reference in their entireties, including all figures thereof.

FIGS. 1-3 highlight some of the features of golf balls of the invention and should not be construed as limiting the scope of the invention. FIG. 1 illustrates one possible golf ball construction incorporating a spherical innermost hollow portion. Referring to FIG. 1, golf ball 2 includes core 3, which is comprised of innermost spherical hollow portion 4, surrounding shell layer 6, and outer core layer 8, formed about shell layer 6. Shell layer 6 is has a non-uniform thickness that is created by a non-uniform contour in inner surface 10 that defines a phantom spherical circumference 11 of innermost spherical hollow portion 4 at symmetrically spaced locations 12. In this embodiment, a plurality of hollow spaces 14 are thereby created adjacent to the phantom spherical circumference 11, with hollow spaces 14 alternating with shell layer 6 symmetrically and circumferentially about innermost spherical hollow portion 4.

Inner surface 10 has an inner surface hardness, and an outer surface 16 of shell layer 6 has an outer surface hardness that is greater than the inner surface hardness to define a first hardness gradient of from about 1 to 7 Shore C. Meanwhile, outer core layer 8 has a second inner surface 18 having a second inner surface hardness, and a second outer surface 20 having a second outer surface hardness that is different than the second inner surface hardness to define a second hardness gradient.

Inner cover layer 22 is disposed about second outer surface 20 of outer core layer 8 and comprises an ionomeric material and has a first hardness that is greater than a second hardness of outer cover layer 24 that is disposed about inner cover layer 22 and comprises a polyurea or a polyurethane.

Alternating hardnesses can therefore be created symmetrically about and adjacent to the innermost spherical hollow portion of the core, resulting in unique playing characteristics, excellent adhesion between layers and excellent continuity of hardness distribution from the innermost hollow portion and radially outward.

Referring to FIG. 2, golf ball 26 includes core 27 which is comprised of innermost spherical hollow portion 28, surrounding shell layer 30, and outer core layer 32, formed about shell layer 30. Shell layer 30 has an inner surface 34, having an inner surface hardness, and an outer surface 36, having an outer surface hardness that is greater than the inner surface hardness by about 1-7 Shore C. Shell layer 30 has a non-uniform thickness that is created by a non-uniform contour of outer surface 36 that borders and defines a contour of a second inner surface 38 of outer core layer 32. The outer surface hardness and a second inner surface hardness of the second inner surface differ and alternate symmetrically and circumferentially about the inner surface of shell layer 30.

Meanwhile, a second outer surface 40 of outer core layer 32 has a second outer surface hardness that is different than the second inner surface hardness to define a second hardness gradient.

Inner cover layer 42 is disposed about second outer surface 40 and comprises an ionomeric material and has a first hardness that is greater than a second hardness of outer cover layer 44, which is disposed about inner cover layer 42 and comprises a polyurea or a polyurethane.

Alternating hardnesses can therefore be created symmetrically at the interface between the shell layer and outer core layer to produce unique playing characteristics with excellent adhesion between layers and also excellent continuity of hardness distribution from innermost hollow portion and radially outward.

Referring to FIG. 3, golf ball 45 includes core 46 that is comprised of innermost aspherical hollow portion 47, shell layer 48, and outer core layer 49. Shell layer 48 has an inner surface 50 and a plurality of symmetrically spaced extensions 52 that border and define the shape of innermost aspherical hollow portion 47. Inner surface 50 has an inner surface hardness, and outer surface 54 of shell layer 48 has an outer surface hardness that is greater than the inner surface hardness to define a first hardness gradient of from about 1 to 7 Shore C. Meanwhile, outer surface 54 has a non-uniform contour that borders and defines a contour of a second inner surface 56 of outer core layer 49. The outer surface hardness and a second inner surface hardness of second inner surface 56 differ and alternate symmetrically and circumferentially about the inner surface.

Meanwhile, a second outer surface 58 of outer core layer 49 has a second outer surface hardness that is different than the second inner surface hardness to define a second hardness gradient.

Inner cover layer 60 is disposed about second outer surface 58 and comprises an ionomeric material and has a first hardness that is greater than a second hardness of outer cover layer 62, which is disposed about inner cover layer 60 and comprises a polyurea or a polyurethane.

Alternating hardnesses can therefore be created symmetrically at the interface between the shell layer and outer core layer, to achieve unique playing characteristics with excellent adhesion between layers and also excellent continuity of hardness distribution from innermost hollow portion and radially outward.

Examples of particular embodiments of a golf ball of the invention, incorporating a shell layer having a non-uniform thickness as defined herein, may be as follows. In one embodiment, the hollow core of a golf ball of the invention includes a thermoset shell layer containing or encasing an innermost spherical hollow portion. In one embodiment, the thermoset shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material. In another embodiment, the thermoset shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoset material. In yet another embodiment, the thermoset shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoplastic material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material. In still another embodiment, the thermoset shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoplastic material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoset material.

Alternatively, the shell layer may comprise a thermoplastic material. For example, in one embodiment, the hollow core includes a thermoplastic shell layer containing or encasing the innermost spherical hollow portion. In one embodiment, the thermoplastic shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material. In another embodiment, the thermoplastic shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is also formed from a thermoset material. In yet another embodiment, the thermoplastic shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoplastic material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material. In still another embodiment, the thermoplastic shell layer is surrounded by at least two outer core layers, where one outer core layer is formed from a thermoplastic material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoset material.

In one preferred embodiment, the golf ball includes a hollow core formed from a thermoset rubber shell layer encasing an innermost spherical hollow portion. In this embodiment, a single outer core layer is formed around the shell layer to create the hollow golf ball core. The outer core layer is also formed from a thermoset material, which may be the same rubber composition as the shell layer but is preferably a different thermoset rubber composition. A single cover layer or multiple cover layers are formed over the hollow core. Preferably, an inner cover layer and an outer cover layer are formed over the outer core layer. In one embodiment, the inner cover includes an ionomeric material and the outer cover layer includes a polyurea or, preferably, a polyurethane. The outer cover layer is typically softer than the inner cover layer, such as where the inner cover has a hardness of greater than about 60 Shore D and the outer cover layer has a hardness of less than about 60 Shore D.

In the above embodiment, the innermost spherical hollow portion preferably has a diameter of about 0.51 to 1.1 inches. The surface hardness of the shell layer may be greater than the inner surface hardness by about 3 to 25 Shore C to define the first hardness gradient. In a preferred embodiment, the thermoset outer core layer has a hardness gradient that is different from the hardness gradient of the thermoset shell layer. Most preferably, the shell layer has a surface hardness greater than about 55 Shore C.

The thermoset shell layer has a coefficient of restitution (COR) less than about 0.750 when measured at an incoming velocity of 125 ft/s. Preferably, the COR is less than about 0.700, more preferably about 0.500 to 0.700, and most preferably about 0.600 to 0.700. The overall hollow core (the combination of the thermoset shell layer and the thermoset outer core layer) has a COR, measured at an incoming velocity of 125 ft/s, higher than the COR of the inner core shell layer by greater than about 5%, more preferably about 10 to 50%, and most preferably about 15 to 30%.

In an alternative embodiment, the hardness gradient of the thermoset outer core layer has a ‘zero hardness gradient’. The zero hardness gradient is typically about 0 Shore C (defined herein as ±2 Shore C). The hardness gradient of the thermoset outer core layer may also have a ‘negative hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C. The hardness gradient of the thermoset outer core layer may also have a ‘positive hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C.

The golf ball has a first volume and the hollow center has a second volume. The volume of the hollow center is about 2% to 30% of the golf ball volume, more preferably about 5% to 25% of the golf ball volume, and most preferably about 10% to 20% of the golf ball volume.

Examples of suitable hardness profiles for cores in golf balls of the invention may be found in related U.S. patent application Ser. Nos. 13/736,993, 13/736,997, 13/737,026, and 13/737,041, each filed on Jan. 9, 201, and any accompanying FIGS. 1a and 1b thereof, all incorporated by reference herein as stated further above.

Golf balls of the invention may also include an aspherical hollow volume in the center of the golf ball, formed by a shell layer that meanwhile has a non-uniform contour in the shell layer outer surface. In such a golf ball of the invention, the shell layer has a plurality of hollow spaces therein that extend from an inner surface to an outer surface of the shell layer, and meanwhile also has a plurality of extensions located on an inner surface that border and define the shape of the aspherical hollow volume rather than a separate insert having hollow spaces that form the aspherical hollow volume. The plurality of extensions and innermost hollow portion, combined, form a phantom sphere having an aspherical hollow volume within. Manufacturing costs are meanwhile also reduced since an aspherical hollow core is constructed such that the aspherical hollow volume and shell layer are unitary.

Accordingly, in one embodiment of a golf ball of the invention, the core comprises: an innermost aspherical hollow portion having a volume V_(ahp); a shell layer that is formed from a thermoplastic or thermoset composition and has an inner surface comprising a plurality of symmetrically spaced extensions that border and define the shape of the innermost aspherical hollow portion; and at least one outer core layer formed from a thermoset or thermoplastic composition disposed about the shell layer. The plurality of extensions and innermost aspherical hollow portion, combined, form a phantom sphere having a diameter of from about 0.10 inches to about 1.1 inches; and the plurality of extensions have a combined total volume E_(TV) such that V_(ahp)≧E_(TV)>0.20(E_(TV)+V_(ahp)). As defined above, the plurality of extensions have a combined volume E_(TV) that is equal to or less than volume V_(ahp) of the innermost aspherical hollow portion but greater than 20% of the total volume E_(TV)+V_(ahp) of the plurality of extensions and innermost aspherical hollow portion, combined.

In alternative embodiments, the combined volume E_(TV) of the extensions may be such that V_(ahp)≧E_(TV)>0.25(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>0.30(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>0.35(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>0.40(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>0.45(E_(TV)+V_(ahp)). In still other embodiments, V_(ahp)≧E_(TV)>˜0.20(E_(TV)+V_(ahp)), V_(ahp)≧E_(TV)>˜0.25(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>618 0.30(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>˜0.35(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>˜0.40(E_(TV)+V_(ahp)), or V_(ahp)≧E_(TV)>˜0.45(E_(TV)+V_(ahp)).

The plurality of extensions and innermost aspherical hollow portion, combined, form a phantom sphere having a volume that is defined by the maximum radial distance of the innermost aspherical hollow portion. The diameter of the phantom sphere may alternatively be from about 0.20 inches to about 1.1 inches, or from about 0.20 inches to about 0.90 inches, or from about 0.25 inches to about 0.75 inches, or from about 0.30 inches to about 0.50 inches, or from about 0.20 inches to about 1.0 inches, or from about 0.25 inches to about 0.90 inches, or from about 0.30 inches to about 0.90 inches. In one embodiment, the plurality of extensions and innermost aspherical hollow portion, combined, has a diameter of greater than 0.5 inches, or greater than about 1.0 inches.

Meanwhile, the shell layer has an outer surface with a non-uniform contour. Additionally, the inner surface has an inner surface hardness and the outer surface has an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient; and the outer core layer has a second hardness gradient.

The shell layer may have a maximum thickness, including extensions, of up to about 0.40 inches, or up to about 0.375 inches, or up to about 0.30 inches, or up to about 0.275 inches, or up to about 0.200 inches, or up to about 0.175 inches. In one embodiment, wherein the shell layer is relatively thick, the shell layer maximum thickness is from about 0.125 inches to about 0.375 inches, or from about 0.2 inches to about 0.3125 inches, or from about 0.25 inches to about 0.3 inches, or from about 0.26 inches to about 0.275 inches.

In some embodiments, the shell layer may have a thickness at locations not containing extensions of greater than about 0.01 inches but less than the maximum thickness. When the shell layer is desired to be relatively thin at locations not containing extensions, that thickness may be from about 0.01 inches to about 0.1 inches, or from about 0.02 inches to about 0.075 inches, or from about 0.025 inches to about 0.04 inches, or from about 0.03 inches to about 0.035 inches.

When the shell layer is relatively thin and formed from a thermoplastic material, the thermoplastic material is preferably selected to be somewhat heat resistant (or blended with a heat resistant thermoplastic material) to avoid melting of the layer by subsequent molding of additional core and/or cover layers.

With the dimensions of the hollow interior in mind, the hollow cores (innermost aspherical hollow portion, shell layer and outer core layer(s)) of the invention may have an outer diameter of about 0.75 inches to about 1.62 inches, or about 0.75 inches to about 1.58 inches, or about 1.0 inches to about 1.57 inches, or about 1.3 inches to about 1.56 inches, or about 1.4 inches to about 1.55 inches. The shell layer may have an outer diameter of about 0.75 inches, 1.0 inches, 1.20 inches, or 1.30 inches, with one outer diameter being 0.75 inches, or 1.0 inches.

In an alternative embodiment, the outer core layer should have an outer diameter (the entire hollow core, shell layer plus outer core layer) of about 1.30 inches to about 1.62 inches, or 1.4 inches to about 1.6 inches, or about 1.5 inches to about 1.59 inches. In some embodiments, the outer core layer has an outer diameter of about 1.51 inches, 1.53 inches, or 1.550 inches.

The inner and outer cover layers may for example have a thickness of about 0.010 to 0.080 inches, or about 0.015 to 0.060 inches, or about 0.020 to 0.040 inches. Alternatively, the inner and outer cover layers have a thickness of about 0.015 inches to about 0.055 inches, or about 0.02 inches to about 0.04 inches, or about 0.025 inches to about 0.035 inches. The inner cover layer, if present, may have a hardness of about 60 Shore D or greater, or about 65 Shore D or greater, or about 70 Shore D or greater. The inner cover layer may harder than the outer cover layer although embodiments are envisioned wherein the outer cover layer is harder than the inner cover layer. The outer cover layer may have a hardness of about 60 Shore D or less, or about 55 Shore D or less, or about 50 Shore D or less.

FIGS. 1-6 of related U.S. patent application Ser. No. 14/959,190, filed on Dec. 4, 2015 (incorporated by reference herein in its entirety above) provide examples of some suitable constructions for shell layers forming aspherical innermost hollow portions, etc.

In golf balls of the present invention, any of the core, cover, or intermediate layer may include more than one layer.

In one embodiment, the hollow core is formed of a thermoset shell layer that borders and defines the innermost aspherical hollow portion. In another embodiment, the hollow core is formed from a thermoset shell layer and at least two outer core layers, wherein an outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material. In an alternative embodiment, the hollow core includes a thermoset shell layer and at least two outer core layers, wherein an outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoset material.

The hollow core may alternatively be formed of a thermoplastic shell layer that borders and defines the shape of the innermost aspherical hollow portion. In another embodiment, the hollow core includes the thermoplastic shell layer and at least two outer core layers, wherein an outer core layer is formed from a thermoplastic material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoset material. In an alternative embodiment, the hollow core includes the thermoplastic shell layer and at least two outer core layers, wherein an outer core layer is formed from a thermoplastic material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material.

The shell, outer core, or intermediate core layers may have either a conventional “hard-to-soft” hardness gradient (i.e., the outermost surface/portion of the layer is harder than the innermost surface/portion), known as a “positive hardness gradient,” or a “soft-to-hard” hardness gradient (i.e., a “negative” hardness gradient) as measured radially-inward from the outer surface or portion of each component towards the innermost portion (i.e., from the outer surface/portion towards the inner surface/portion of the shell and/or core layers). As used herein, the terms “negative” and “positive,” with respect to hardness gradient, refer to the result of subtracting the hardness value at the innermost portion of the component being measured (e.g., the inner surface of a core layer) from the hardness value at the outer surface of the component being measured (e.g., the outer surface of an outer core layer). For example, if the outer surface of a core layer has a lower hardness value than at the inner surface, the hardness gradient will be deemed a “negative” gradient (a smaller number−a larger number=a negative number), although the magnitude may be disclosed in the application as the absolute value of the subtraction result in combination with the designation ‘negative’).

The thermoplastic shell, intermediate core layers, and outer core layers of the invention may have ‘positive hardness gradients’ or ‘negative hardness gradients’, as described above. Alternatively, the thermoplastic layers may have a ‘zero hardness gradient’, defined herein to include a 0 Shore C hardness gradient±2 Shore C. The thermoplastic layer ‘positive hardness gradient’ or ‘negative hardness gradient’ may be from about 0 Shore C to about 10 Shore C, or about 2 Shore C to about 8 Shore C, or about 3 Shore C to about 5 Shore C.

The thermoset shell, intermediate core layers, and outer core layers of the invention may have ‘positive hardness gradients’ or ‘negative hardness gradients’, as described above. Alternatively, the thermoset layers may have a ‘zero hardness gradient’, defined herein to include a 0 Shore C hardness gradient±2 Shore C. The thermoset layer ‘positive hardness gradient’ or ‘negative hardness gradient’ may be from about 1 Shore C to about 30 Shore C, or about 2 Shore C to about 27 Shore C, or about 5 Shore C to about 25 Shore C, or about 10 to 20 Shore C. Other suitable thermoset ‘positive hardness gradient’ or ‘negative hardness gradient’ core layers can be found in U.S. Pat. Nos. 7,537,529 and 7,537,530, the disclosures of which are incorporated herein, in their entirety, by reference thereto.

A variety of the above thermoset and thermoplastic hardness gradient layers are envisioned and both ‘positive hardness gradients’ and/or ‘negative hardness gradients’ may be combined to form the hollow cores of the invention having various layers of this nature.

The surface hardness of the shell or core layers is obtained from the average of a number of measurements taken from opposing hemispheres of the particular layer, taking care to avoid making measurements on the parting line or any surface defects, such as holes or protrusions. Hardness measurements are made pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic by Means of a Durometer.” Because of the curved surface of the hollow core or core layers, care must be taken to insure that they are centered under the durometer indentor before a surface hardness reading is obtained. A calibrated, digital durometer, capable of reading to 0.1 hardness units is used for all hardness measurements and is set to take hardness readings 1 second after the maximum reading is obtained. The digital durometer must be attached to, and its foot made parallel to, the base of an automatic stand, such that the weight on the durometer and attack rate conform to ASTM D-2240.

To prepare the hollow core for hardness and hardness gradient measurements, the core (shell layer or with one or two core layers) is gently pressed into a hemispherical holder having an internal diameter approximately slightly smaller than the diameter of the core, such that the core is held in place in the hemispherical portion of the holder while concurrently leaving the geometric central plane of the core exposed. The core is secured in the holder by friction, such that it will not move during the cutting and grinding steps, but the friction is not so excessive that distortion of the natural shape of the core would result. The core is secured such that the parting line of the core is roughly parallel to the top of the holder. The diameter of the core is measured 90° to this orientation prior to securing. A measurement is also made from the bottom of the holder to the top of the core to provide a reference point for future calculations. A rough cut, made slightly above the exposed geometric center of the core using a band saw or other appropriate cutting tool, making sure that the core does not move in the holder during this step. The remainder of the core, still in the holder, is secured to the base plate of a surface grinding machine. The exposed ‘rough’ core surface is ground to a smooth, flat surface, revealing the hollow portion of the core, which can be verified by measuring the height of the bottom of the holder to the exposed surface of the core, making sure that exactly half of the original height of the core, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with a center square and carefully marked and the hardness is measured at the center mark. Hardness measurements at any distance from the center of the core may be measured by drawing a line radially outward from the center mark, and measuring and marking the distance from the center, typically in 1- or 2-mm increments. All hardness measurements performed on the plane passing through the hollow portion are performed while the core is still in the holder and without having disturbed its orientation, such that the test surface is constantly parallel to the bottom of the holder. The hardness difference from any predetermined location on the core is calculated as the average surface hardness minus the hardness at the appropriate reference point.

One or more of the shell layer and/or core layers may be formed from a composition including at least one thermoset base rubber, such as a polybutadiene rubber, cured with at least one peroxide and at least one reactive co-agent, which can be a metal salt of an unsaturated carboxylic acid, such as acrylic acid or methacrylic acid, a non-metallic coagent, or mixtures thereof. Preferably, a suitable antioxidant is included in the composition. An optional ‘soft and fast agent’ (sometimes called a cis-to-trans catalyst), such as an organosulfur or metal-containing organosulfur or thiol compound, can also be included in the core formulation. Other ingredients that are known to those skilled in the art may be used, and are understood to include, but not be limited to, density-adjusting fillers, process aides, plasticizers, blowing or foaming agents, sulfur accelerators, and/or non-peroxide radical sources.

The base thermoset rubber, which can be blended with other rubbers and polymers, typically includes a natural or synthetic rubber. For example, the base rubber can be 1,4-polybutadiene having a cis structure of at least 40%, preferably greater than 80%, and more preferably greater than 90%.

Examples of desirable polybutadiene rubbers include BUNA® CB22 and BUNA® CB23, CB1221, CB1220, CB24, and CB21, commercially-available from LANXESS Corporation; UBEPOL® 360L and UBEPOL® 150L and UBEPOL-BR rubbers, commercially available from UBE Industries, Ltd. of Tokyo, Japan; KINEX® 7245, KINEX® 7265, and BUDENE 1207 and 1208, commercially available from Goodyear of Akron, Ohio; SE BR-1220; Europrene® NEOCIS® BR 40 and BR 60, commercially available from Polimeri Europa; and BR 01, BR 730, BR 735, BR 11, and BR 51, commercially available from Japan Synthetic Rubber Co., Ltd; PETROFLEX® BRNd-40; and KARBOCHEM® ND40, ND45, and ND60, commercially available from Karbochem.

From the Lanxess Corporation, are for example the Nd- and Co-catalyzed grades, but all of the following may be used: BUNA CB 21; BUNA CB 22; BUNA CB 23; BUNA CB 24; BUNA CB 25; BUNA CB 29 MES; BUNA CB Nd 40; BUNA CB Nd 40 H; BUNA CB Nd 60; BUNA CB 55 NF; BUNA CB 60; BUNA CB 45 B; BUNA CB 55 B; BUNA CB 55 H; BUNA CB 55 L; BUNA CB 70 B; BUNA CB 1220; BUNA CB 1221; BUNA CB 1203; BUNA CB 45. Additionally, numerous suitable rubbers are available from JSR (Japan Synthetic Rubber), UBEPOL sold by Ube Industries Inc, Japan, BST sold by BST Elastomers, Thailand; IPCL sold by Indian Petrochemicals Ltd, India; NITSU sold by Karbochem or Karbochem Ltd of South Africa; PETROFLEX of Brazil; LG of Korea; and Kuhmo Petrochemical of Korea.

The base rubber may also comprise high or medium Mooney viscosity rubber, or blends thereof. A “Mooney” unit is a unit used to measure the plasticity of raw or unvulcanized rubber and is defined according to ASTM D-1646. The Mooney viscosity range may for example be greater than about 40, or in the range of from about 40 to 60, or in the range from about 40 to 52.

Commercial sources of suitable polybutadienes include Bayer AG CB23 (Nd-catalyzed), which has a Mooney viscosity of around 50 and is a highly linear polybutadiene, and CB1221 (Co-catalyzed). If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as other polybutadiene rubbers, natural rubber, styrene butadiene rubber, and/or isoprene rubber in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are typically based on 100 parts by weight of the total elastomer mixture.

In one embodiment, the base rubber comprises a Nd-catalyzed polybutadiene, a rare earth-catalyzed polybutadiene rubber, or blends thereof. If desired, the polybutadiene can also be mixed with other elastomers known in the art such as natural rubber, polyisoprene rubber and/or styrene-butadiene rubber in order to modify the properties of the core. Other suitable base rubbers include thermosetting materials such as, ethylene propylene diene monomer rubber, ethylene propylene rubber, butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber, nitrile rubber, and silicone rubber.

Suitable peroxide initiating agents include dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne; 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; 2,2′-bis(t-butylperoxy)-di-iso-propylbenzene; 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl 4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide; n-butyl 4,4′-bis(butylperoxy)valerate; di-t-butyl peroxide; or 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butyl hydroperoxide, α-α bis(t-butylperoxy)diisopropylbenzene, di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butyl peroxide. For example, the rubber composition may include from about 0.25 to about 5.0 parts by weight peroxide per 100 parts by weight rubber (phr), or 0.5 phr to 3 phr, or 0.5 phr to 1.5 phr. In one embodiment, the peroxide is present in an amount of about 0.8 phr. These ranges of peroxide are given assuming the peroxide is 100% active, without accounting for any carrier that might be present. Because many commercially available peroxides are sold along with a carrier compound, the actual amount of active peroxide present must be calculated. Commercially-available peroxide initiating agents include DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™ 40C and DICUP™ 40KE) available from Crompton (Geo Specialty Chemicals). Similar initiating agents are available from AkroChem, Lanxess, Flexsys/Harwick and R. T. Vanderbilt. Another commercially-available initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, which is a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane and di(2-t-butylperoxyisopropyl)benzene. TRIGONOX™ peroxides are generally sold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal salts of diacrylates, dimethacrylates, and monomethacrylates suitable for use in this invention include those wherein the metal is zinc, magnesium, calcium, barium, tin, aluminum, lithium, sodium, potassium, iron, zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but the present invention is not limited thereto. ZDA provides golf balls with a high initial velocity. The ZDA can be of various grades of purity. For the purposes of this invention, the lower the quantity of zinc stearate present in the ZDA the higher the ZDA purity. ZDA containing less than about 10% zinc stearate is preferable. More preferable is ZDA containing about 4-8% zinc stearate. Suitable, commercially available zinc diacrylates include those from Sartomer Co. Examples of concentrations of ZDA that can be used are about 10 phr to about 40 phr, or 20 phr to about 35 phr, or 25 phr to about 35 phr. In one embodiment, the reactive co-agent is present in an amount of about 29 phr to about 31 phr.

Additional co-agents that may be used alone or in combination with those mentioned above include, but are not limited to, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, and the like. It is understood by those skilled in the art, that in the case where these co-agents may be liquids at room temperature, it may be advantageous to disperse these compounds on a suitable carrier to promote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidative breakdown of elastomers, and/or inhibit or prevent reactions that are promoted by oxygen radicals. Some exemplary antioxidants that may be used in the present invention include, but are not limited to, quinoline type antioxidants, amine type antioxidants, and phenolic type antioxidants. A preferred antioxidant is 2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPC from R. T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T, VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Suitable antioxidants include, but are not limited to, alkylene-bis-alkyl substituted cresols; substituted phenols; alkylene bisphenols; and alkylene trisphenols. The antioxidant is typically present in an amount of about 0.1 phr to 5 phr, or from about 0.1 phr to 2 phr, or about 0.1 phr to 1 phr. In an alternative embodiment, the antioxidant should be present in an amount to ensure that the hardness gradient of the core layers is “negative.” For example, about 0.2 phr to 1 phr antioxidant may be added to the core layer formulation, or about 0.3 to 0.8 phr, or 0.4 to 0.7 phr. About 0.25 phr to 1.5 phr of peroxide as calculated at 100% active can be added to the core formulation, or about 0.5 phr to 1.2 phr, or about 0.7 phr to 1.0 phr. The ZDA amount can be varied to suit the desired compression, spin and feel of the resulting golf ball. The cure regime can have a temperature range from about 290° F. to 350° F., or about 300° F. to 335° F., and the stock is held at that temperature for about 10 minutes to 30 minutes fore example.

The thermoset rubber compositions may also include an optional ‘soft and fast agent’. As used herein, “soft and fast agent” means any compound or a blend thereof that that is capable of making a core 1) be softer (lower compression) at constant COR or 2) have a higher COR at equal compression, or any combination thereof, when compared to a core equivalently prepared without a soft and fast agent. The thermoset core layer compositions may for example contain about 0.05 phr to 10.0 phr soft and fast agent. In one embodiment, the soft and fast agent is present in an amount of about 0.05 phr to 3.0 phr, or about 0.05 phr to 2.0 phr, or about 0.05 phr to 1.0 phr. In another embodiment, the soft and fast agent is present in an amount of about 2.0 phr to 5.0 phr, or about 2.35 phr to 4.0 phr, or about 2.35 phr to 3.0 phr. Suitable soft and fast agents include, but are not limited to, organosulfur or metal-containing organosulfur compounds, an organic sulfur compound, including mono, di, and polysulfides, a thiol, or mercapto compound, an inorganic sulfide compound, a Group VIA compound, or mixtures thereof. The soft and fast agent component may also be a blend of an organosulfur compound and an inorganic sulfide compound.

Fillers may be added to the thermoset rubber layer compositions typically include, but are not limited to, processing aids and/or compounds to affect rheological and mixing properties, density-modifying fillers, tear strength, or reinforcement fillers, and the like. Fillers include materials such as tungsten, zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, metals, metal oxides and salts, regrind (recycled core material typically ground to about 30 mesh particle size), high-Mooney-viscosity rubber regrind, trans-rubber regrind (recycled core material containing high trans isomer of polybutadiene), and the like. When trans-regrind is present, the amount of trans isomer can preferably be between about 10% and 60%. The fillers are generally inorganic and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, an array of silicas, and mixtures thereof. Fillers may also include various foaming agents or blowing agents which may be readily selected by one of ordinary skill in the art. Fillers may include polymeric, ceramic, metal, and glass microspheres may be solid or hollow, and filled or unfilled. Fillers may be added to one or more layers of the golf ball to modify the density thereof.

The thermoset rubber shell and/or core layers may optionally include at least one additive and/or filler. These materials are also suitable for inclusion in the thermoplastic layers of the present invention. Suitable additives and fillers include, but are not limited to, chemical blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, antioxidants, stabilizers, softening agents, fragrance components, plasticizers, impact modifiers, TiO₂, acid copolymer wax, surfactants, performance additives (e.g., A-C performance additives, particularly A-C low molecular weight ionomers and copolymers, A-C oxidized polyethylenes, and A-C ethylene vinyl acetate waxes, commercially available from Honeywell International Inc.), fatty acid amides (e.g., ethylene bis-stearamide and ethylene bis-oleamide), fatty acids and salts thereof (e.g., stearic acid, oleic acid, zinc stearate, magnesium stearate, zinc oleate, and magnesium oleate), and fillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinc carbonate, barium carbonate, tungsten, tungsten carbide, silica, lead silicate, regrind, clay, mica, talc, nano-fillers, carbon black, glass flake, milled glass, flock, fibers, and mixtures thereof. Suitable additives are more fully described in, U.S. Pat. No. 7,041,721 which issued on May 9, 2006, the disclosure of which is hereby incorporated herein by reference. In a particular embodiment, the total amount of additive(s) and filler(s) present in the particle composition is 20 wt % or less, or 15 wt % or less, or 12 wt % or less, or 10 wt % or less, or 9 wt % or less, or 6 wt % or less, or 5 wt % or less, or 4 wt % or less, or 3 wt % or less, or within a range having a lower limit of 0 or 2 or 3 or 5 wt %, based on the total weight of the particle composition, and an upper limit of 9 or 10 or 12 or 15 or 20 wt %, based on the total weight of the particle composition. In a particular aspect of this embodiment, the particle composition includes fillers selected from carbon black, micro- and nano-scale clays and organoclays, including (e.g., CLOISITE and NANOFIL nanoclays, commercially available from Southern Clay Products, Inc.; NANOMAX and NANOMER nanoclays, commercially available from Nanocor, Inc., and PERKALITE nanoclays, commercially available from Akzo Nobel Polymer Chemicals), micro- and nano-scale talcs (e.g., LUZENAC HAR high aspect ratio talcs, commercially available from Luzenac America, Inc.), glass (e.g., glass flake, milled glass, microglass, and glass fibers), micro- and nano-scale mica and mica-based pigments (e.g., IRIODIN pearl luster pigments, commercially available from The Merck Group), and combinations thereof. Particularly suitable combinations of fillers include, but are not limited to, micro-scale fillers combined with nano-scale fillers, and organic fillers with inorganic fillers.

Alternatively, the thermoset layers herein may be formed from a castable, pourable reactive material such as a castable polyurea or a castable polyurethane; castable hybrid poly(urethane/urea); and castable hybrid poly(urea/urethane). Suitable polyurethanes include for example those disclosed in U.S. Pat. Nos. 5,334,673 and 6,506,851. Suitable polyureas include for example those disclosed in U.S. Pat. Nos. 5,484,870 and 6,835,794. These patents are incorporated herein by reference thereto.

For the thermoset layers of the invention, the fillers and/or additives are present in an amount of about 50 wt % or less, or 30 wt % or less, or 20 wt % or less, or 15 wt % or less, based on the total weight of the composition. Alternatively, for the thermoplastic layers of the invention, the fillers and/or additives are present in an amount of about 10 wt % or less, or 6 wt % or less, or 3 wt % or less, based on the total weight of the composition.

The particle composition optionally includes one or more melt flow modifiers. Suitable melt flow modifiers include materials which increase the melt flow of the composition, as measured using ASTM D-1238, condition E, at 190° C., using a 2160-g weight. Examples of suitable melt flow modifiers include, but are not limited to, fatty acids and fatty acid salts, including, but not limited to, those disclosed in U.S. Pat. No. 5,306,760, the disclosure of which is hereby incorporated herein by reference; fatty amides and salts thereof; polyhydric alcohols, including, but not limited to, those disclosed in U.S. Pat. Nos. 7,365,128 and 8,163,823, the entire disclosures of which are hereby incorporated herein by reference; polylactic acids, including, but not limited to, those disclosed in U.S. Pat. No. 7,642,319, the disclosure of which is hereby incorporated herein by reference; and the modifiers disclosed in U.S. Pat. No. 8,163,823 and U.S. Patent Application Publication No. 2009/0203469, the disclosures of which are hereby incorporated herein by reference. Flow enhancing additives also include, but are not limited to, montanic acids, esters of montanic acids and salts thereof, bis-stearoylethylenediamine, mono- and polyalcohol esters such as pentaerythritol tetrastearate, zwitterionic compounds, and metallocene-catalyzed polyethylene and polypropylene wax, including maleic anhydride modified versions thereof, amide waxes and alkylene diamides such as bistearamides. Particularly suitable fatty amides include, but are not limited to, saturated fatty acid monoamides (e.g., lauramide, palmitamide, arachidamide behenamide, stearamide, and 12-hydroxy stearamide); unsaturated fatty acid monoamides (e.g., oleamide, erucamide, and ricinoleamide); N-substituted fatty acid amides (e.g., N-stearyl stearamide, N-behenyl behenamide, N-stearyl behenamide, N-behenyl stearamide, N-oleyl oleamide, N-oleyl stearamide, N-stearyl oleamide, N-stearyl erucamide, erucyl erucamide, and erucyl stearamide, N-oleyl palmitamide, methylol amide (preferably methylol stearamide, methylol behenamide); saturated fatty acid bis-amides (e.g., methylene bis-stearamide, ethylene bis-stearamide, ethylene bis-isostearamide, ethylene bis-hydroxystearamide, ethylene bis-behenamide, hexamethylene bis-stearamide, hexamethylene bis-behenamide, hexamethylene bis-hydroxystearamide, N,N′-distearyl adipamide, and N,N′-distearyl sebacamide); unsaturated fatty acid bis-amides (e.g., ethylene bis-oleamide, hexamethylene bis-oleamide, N,N′-dioleyl adipamide, N,N′-dioleyl sebacamide); and saturated and unsaturated fatty acid tetra amides, stearyl erucamide, ethylene bis stearamide and ethylene bis oleamide. Suitable examples of commercially available fatty amides include, but are not limited to, KEMAMIDE fatty acids, such as KEMAMIDE B (behenamide/arachidamide), KEMAMIDE W40 (N,N′-ethylenebisstearamide), KEMAMIDE P181 (oleyl palmitamide), KEMAMIDE S (stearamide), KEMAMIDE U (oleamide), KEMAMIDE E (erucamide), KEMAMIDE O (oleamide), KEMAMIDE W45 (N,N′-ethylenebisstearamide), KENAMIDE W20 (N,N′-ethylenebisoleamide), KEMAMIDE E180 (stearyl erucamide), KEMAMIDE E221 (erucyl erucamide), KEMAMIDE S180 (stearyl stearamide), KEMAMIDE 5221 (erucyl stearamide), commercially available from Chemtura Corporation; and CRODAMIDE fatty amides, such as CRODAMIDE OR (oleamide), CRODAMIDE ER (erucamide), CRODAMIDE SR (stereamide), CRODAMIDE BR (behenamide), CRODAMIDE 203 (oleyl palmitamide), and CRODAMIDE 212 (stearyl erucamide), commercially available from Croda Universal Ltd.

The shell layer, and intermediate and outer core layers of the hollow golf ball may also be formed from thermoplastic materials such as ionomeric polymers, and highly- and fully-neutralized ionomers (HNP). Acid moieties of the HNP's, typically ethylene-based ionomers, can be neutralized greater than about 80%, or greater than about 90%, or even about 100% or greater. The HNP's can be also be blended with a second polymer component, which, if containing an acid group, may be neutralized in a conventional manner, by the organic fatty acids of the present invention, or both. The second polymer component, which may be partially- or fully-neutralized, may comprise ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, metallocene-catalyzed polymers (grafted and non-grafted), single-site polymers, high-crystalline acid polymers, cationic ionomers, and the like. HNP polymers typically have a material hardness of between about 20 and about 80 Shore D, and a flexural modulus of between about 3,000 psi and about 200,000 psi.

The HNP's may be ionomers and/or their acid precursors that are neutralized, either fully or partially, with organic acid copolymers or the salts thereof. The acid copolymers are often preferably α-olefin, such as ethylene, C₃₋₈ α,β-ethylenically unsaturated carboxylic acid, such as acrylic and methacrylic acid, copolymers. They may optionally contain a softening monomer, such as alkyl acrylate and alkyl methacrylate, wherein the alkyl groups have from 1 to 8 carbon atoms.

The acid copolymers can be described as E/X/Y copolymers where E is ethylene, X is an α,β-ethylenically unsaturated carboxylic acid, and Y is a softening comonomer. In a preferred embodiment, X is acrylic or methacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. X is often preferably present in an amount from about 1 to about 35 weight percent of the polymer, or from about 5 to about 30 weight percent of the polymer, or from about 10 to about 20 weight percent of the polymer. Y is often preferably present in an amount from about 0 to about 50 weight percent of the polymer, or from about 5 to about 25 weight percent of the polymer, or from about 10 to about 20 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are not limited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containing ethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylic acid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylate copolymers. The most preferred acid-containing ethylene copolymers are, ethylene/(meth)acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylic acid/methyl acrylate copolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na, Mg, K, Ca, or Zn. It has been found that by adding sufficient organic acid or salt of organic acid, along with a suitable base, to the acid copolymer or ionomer, however, the ionomer can be neutralized, without losing processability, to a level much greater than for a metal cation. The acid moieties may be neutralized greater than about 80%, or from 90-100%, or 100% or greater without losing processability. This accomplished by melt-blending an ethylene α,β-ethylenically unsaturated carboxylic acid copolymer, for example, with an organic acid or a salt of organic acid, and adding a sufficient amount of a cation source to increase the level of neutralization of all the acid moieties (including those in the acid copolymer and in the organic acid) to greater than 90%, or greater than 100%.

The organic acids are typically aliphatic, mono- or multi-functional (saturated, unsaturated, or multi-unsaturated) organic acids. Salts of these organic acids may also be employed. The salts of organic acids of the present invention include the salts of barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, or calcium, salts of fatty acids, particularly stearic, behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It is preferred that the organic acids and salts of the present invention be relatively non-migratory (they do not bloom to the surface of the polymer under ambient temperatures) and non-volatile (they do not volatilize at temperatures required for melt-blending).

The ionomers of the invention may also be more conventional ionomers, i.e., partially-neutralized with metal cations. The acid moiety in the acid copolymer may be neutralized about 1 to about 90%, or at least about 20 to about 75%, or at least about 40 to about 70%, to form an ionomer, by a cation such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or a mixture thereof.

Examples of thermoplastic materials are disclosed in U.S. Pat. No. 7,591,742, the disclosure of which is incorporated herein in its entirety by reference thereto.

Thermoplastic elastomers (TPE) many also be used for the thermoplastic shell or core layers and/or to modify the properties of the shell and/or core layers, or the uncured rubber core layer stock by blending with the base thermoset rubber. These TPEs include natural or synthetic balata, or high trans-polyisoprene, high trans-polybutadiene, or any styrenic block copolymer, such as styrene ethylene butadiene styrene, styrene-isoprene-styrene, etc., a metallocene or other single-site catalyzed polyolefin such as ethylene-octene, or ethylene-butene, or thermoplastic polyurethanes (TPU), including copolymers, e.g. with silicone. Other suitable TPEs for blending with the thermoset rubbers of the present invention include PEBAX®, which is believed to comprise polyether amide copolymers, HYTREL®, which is believed to comprise polyether ester copolymers, thermoplastic urethane, and KRATON®, which is believed to comprise styrenic block copolymers elastomers. Any of the TPEs or TPUs above may also contain functionality suitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into the base rubber for the shell and core layers. Examples include, but are not limited to, thermoset elastomers such as core regrind, thermoplastic vulcanizate, copolymeric ionomer, terpolymeric ionomer, polycarbonate, polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols, acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate, polyphenylene ether, impact-modified polyphenylene ether, high impact polystyrene, diallyl phthalate polymer, styrene-acrylonitrile polymer (SAN) (including olefin-modified SAN and acrylonitrile-styrene-acrylonitrile polymer), styrene-maleic anhydride copolymer, styrenic copolymer, functionalized styrenic copolymer, functionalized styrenic terpolymer, styrenic terpolymer, cellulose polymer, liquid crystal polymer, ethylene-vinyl acetate copolymers, polyurea, and polysiloxane or any metallocene-catalyzed polymers of these species.

Suitable polyamides for use as an additional polymeric material in compositions within the scope of the present invention also include resins obtained by: (1) polycondensation of (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) a diamine, such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, or decamethylenediamine, 1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-opening polymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, or 12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam with a dicarboxylic acid and a diamine. Specific examples of suitable polyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12, copolymerized NYLON, NYLON MXD6, and NYLON 46.

Formation of the shell and outer core layers of the invention may be accomplished in a variety of ways, such as those disclosed in U.S. Pat. Nos. 5,480,155; 6,315,683, and 8,262,508, the disclosures of which are incorporated herein, in their entirety, by reference thereto.

In one embodiment, the golf ball of the present invention includes a hollow core. The hollow core is formed from a shell layer that borders and defines the shape of the innermost aspherical hollow portion. The shell layer is formed from a thermoset rubber composition and has an outer surface and an inner surface. In this embodiment, a single outer core layer is formed around the shell layer to create a hollow golf ball core. The outer core layer is also formed from a thermoset material, which may be the same rubber composition as the shell layer but may be a different thermoset rubber composition.

A single cover layer or multiple cover layers may be formed over the thermoset/thermoset hollow core. In one single cover layer embodiment, the cover comprises an ionomer having a hardness of at least 55 Shore D.

Alternatively, in another embodiment, a dual cover construction, an inner cover layer and an outer cover layer are formed over the core. In one embodiment, the inner cover includes an ionomeric material and the outer cover layer includes a polyurea or a polyurethane. The outer cover layer is typically softer than the inner cover layer, such as where the inner cover has a hardness of greater than about 60 Shore D and the outer cover layer has a hardness of less than about 60 Shore D; however, the reverse may be used.

In the above embodiment, the plurality of extensions and innermost aspherical hollow portion, combined, can have a diameter of about 0.51 to 1.1 inches. The surface hardness of the shell layer is preferably greater than the hardness of the inner surface of the shell layer by about 3 to 25 Shore C to define a first hardness gradient. In another embodiment, the thermoset outer core layer has a hardness gradient that is different from the hardness gradient of the thermoset shell layer. Most preferably, the shell layer has a surface hardness greater than about 55 Shore C.

The thermoset shell layer has a coefficient of restitution (COR) less than about 0.750 when measured at an incoming velocity of 125 ft/s. Preferably, the COR is less than about 0.700, more preferably about 0.500 to 0.700, and most preferably about 0.600 to 0.700. The overall hollow core (the combination of the thermoset shell layer and the thermoset outer core layer) has a COR, measured at an incoming velocity of 125 ft/s, higher than the COR of the shell layer by greater than about 5%, more preferably about 10 to 50%, and most preferably about 15 to 30%.

In an alternative embodiment, the hardness gradient of the thermoset outer core layer has a ‘zero hardness gradient’. The zero hardness gradient is typically about 0 Shore C (defined herein as ±2 Shore C). The hardness gradient of the thermoset outer core layer may also have a ‘negative hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C. The hardness gradient of the thermoset outer core layer may also have a ‘positive hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C.

The golf ball has a first volume and the plurality of extensions and innermost aspherical hollow portion, combined, has a second volume. The second volume is about 2% to 30% of the first volume, or the second volume is about 5% to 25% of the first volume, or the second volume is about 10% to 20% of the first volume.

In another embodiment of the invention, the hollow core further includes a thermoplastic intermediate core layer disposed between the thermoset shell layer and the thermoset outer core layer. In still another embodiment, the hollow core further includes a thermoset intermediate core layer disposed between the thermoset shell layer and the thermoset outer core layer. The intermediate core layer may formed from a thermoset rubber composition which is the same or different from the thermoset rubber compositions used to form the thermoset shell layer or the thermoset outer core layer. In these embodiments, the plurality of extensions and innermost aspherical hollow portion, combined, preferably has a diameter of about 0.15 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 10 to 25 Shore C to define a hardness gradient, preferably a ‘positive hardness gradient’. The thermoset outer core layer preferably has a hardness gradient that is different from the hardness gradient of the shell layer or the intermediate layer.

In another embodiment of the invention, the hollow core further includes a thermoplastic intermediate core layer disposed between the thermoplastic shell layer and the thermoplastic outer core layer. In still another embodiment, the hollow core further includes a thermoset intermediate core layer disposed between the thermoplastic shell layer and the thermoplastic outer core layer. The intermediate core layer is preferably formed from a thermoset rubber composition. In these embodiments, the plurality of extensions and innermost aspherical hollow portion, combined, preferably has a diameter of about 0.15 to 1.1 inches, the thermoplastic shell layer has a surface hardness greater than an inner surface hardness by about 1 to 10 Shore C to define a hardness gradient, preferably a ‘positive hardness gradient’. The thermoplastic outer core layer preferably has a hardness gradient that is different from the hardness gradient of the thermoplastic shell layer or the intermediate layer.

The golf ball of the present invention includes a hollow core which is formed from a shell layer having a plurality of extensions that border and shape the innermost aspherical hollow portion. The shell layer is formed from a thermoplastic composition, preferably a conventional ionomer or a fully-neutralized ionomer. The shell layer has an outer surface and an inner surface. A single thermoplastic outer core layer is formed over the shell layer and preferably includes an ionomeric composition. The combination of the thermoplastic shell layer and the thermoplastic outer core layer results in a thermoplastic/thermoplastic hollow core. Typically, an inner cover layer and an outer cover layer are formed over the thermoplastic outer core layer. In one embodiment, the inner cover includes an ionomeric material and the outer cover includes a polyurea or, more preferably, a polyurethane. The outer cover is preferably softer than the inner cover layer.

The plurality of extensions and innermost aspherical hollow portion, combined, has a diameter of about 0.15 to 1.1 inches, preferably about 0.25 to 1.0 inches, more preferably about 0.25 to 0.75 inches, and most preferably about 0.3 to 0.5 inches. The surface hardness of the thermoplastic shell layer is preferably greater than the hardness of the inner surface of the shell layer by about 0 to 5 Shore C to define a hardness gradient. The thermoplastic outer core layer also has a hardness gradient, which is the same as or greater than the hardness gradient of the thermoplastic shell layer. In an alternative embodiment, the hardness gradient of the thermoplastic outer core layer has a ‘zero hardness gradient’. The zero hardness gradient is typically about 0 Shore C (defined herein as ±2 Shore C). The hardness gradient of the thermoplastic outer core layer may also have a ‘negative hardness gradient’, preferably about 1 to 10 Shore C, more preferably about 2 to 8 Shore C, and most preferably about 3 to 5 Shore C. The hardness gradient of the thermoplastic outer core layer may also have a ‘positive hardness gradient’, preferably about 1 to 10 Shore C, more preferably about 2 to 8 Shore C, and most preferably about 3 to 5 Shore C.

The golf ball has a first volume and the plurality of extensions and innermost aspherical hollow portion, combined, has a second volume. The second volume is about 2% to 30% of the first volume, more preferably about 5% to 25% of the first volume, and most preferably about 10% to 20% of the first volume.

The thermoplastic shell layer has a COR less than about 0.750 when measured at an incoming velocity of 125 ft/s. Preferably, the COR is less than about 0.700, more preferably about 0.500 to 0.700, and most preferably about 0.600 to 0.700. The overall hollow core (the combination of the thermoplastic shell layer and the thermoplastic outer core layer has a COR, measured at an incoming velocity of 125 ft/s, higher than the COR of the shell layer by greater than about 5%, more preferably about 10 to 50%, and most preferably about 15 to 30%.

In another embodiment of the invention, the hollow core further includes a thermoplastic intermediate core layer disposed between the thermoplastic shell layer and the thermoplastic outer core layer. In still another embodiment, the hollow core further includes a thermoset intermediate core layer disposed between the thermoplastic shell layer and the thermoplastic outer core layer. The intermediate core layer is preferably formed from a thermoset rubber composition. In these embodiments, the plurality of extensions and innermost aspherical hollow portion, combined, preferably has a diameter of about 0.15 to 1.1 inches, the thermoplastic shell layer has a surface hardness greater than an inner surface hardness by about 1 to 10 Shore C to define a hardness gradient, preferably a ‘positive hardness gradient’. The thermoplastic outer core layer preferably has a hardness gradient that is different from the hardness gradient of the thermoplastic shell layer or the intermediate layer.

The plurality of extensions and innermost aspherical hollow portion, combined, has a diameter of about 0.15 to 1.1 inches, preferably about 0.25 to 1.0 inches, more preferably about 0.25 to 0.75 inches, and most preferably about 0.3 to 0.5 inches. The surface hardness of the thermoplastic shell layer is preferably greater than the hardness of the inner surface of the shell layer by about 1 to 5 Shore C to define a first hardness gradient. The thermoset outer core layer has a second hardness gradient, which is greater than the hardness gradient of the thermoplastic shell layer. In an alternative embodiment, the hardness gradient of the thermoset outer core layer has a ‘zero hardness gradient’. The zero hardness gradient is typically about 0 Shore C (defined herein as ±2 Shore C). The hardness gradient of the thermoset outer core layer may also have a ‘negative hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C. The hardness gradient of the thermoset outer core layer may also have a ‘positive hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C.

In another embodiment of the invention, the hollow core further includes a thermoplastic intermediate core layer disposed between the shell layer and the thermoset outer core layer. The thermoplastic intermediate core layer may be formed from a thermoplastic material that is the same or different from the thermoplastic material of the shell layer. In still another embodiment, the hollow core further includes a thermoset intermediate core layer disposed between the thermoplastic shell layer and the thermoset outer core layer. The intermediate core layer may formed from a thermoset rubber composition which is the same or different from the thermoset rubber composition used to form the thermoset outer core layer. In these embodiments, the plurality of extensions and innermost aspherical hollow portion, combined, preferably has a diameter of about 0.15 to 1.1 inches, the thermoplastic shell layer has a surface hardness greater than an inner surface hardness by about 1 to 5 Shore C to define a first hardness gradient, preferably a ‘positive hardness gradient’, and the thermoset outer core layer or thermoset intermediate core layer has a second hardness gradient.

In another embodiment, the inventive golf ball includes the hollow core. The hollow core includes a shell layer formed from a first thermoset rubber composition. The shell layer has an outer surface, an inner surface, and extensions located on the inner surface that define and shape the innermost aspherical hollow portion. In this embodiment, a single thermoplastic outer core layer is disposed about the shell layer to complete the hollow core. A single cover or, preferably, an inner cover layer is formed around the outer core layer. When an inner cover layer is present, an outer cover layer is formed over the inner cover layer. Most preferably, the inner cover is formed from an ionomeric material and the outer cover layer is formed from a polyurethane material, and the outer cover layer has a hardness that is less than that of the inner cover layer. Preferably, the inner cover has a hardness of greater than about 60 Shore D and the outer cover layer has a hardness of less than about 60 Shore D.

The plurality of extensions and innermost aspherical hollow portion, combined, has a diameter of about 0.15 to 1.1 inches, preferably about 0.25 to 1.0 inches, more preferably about 0.25 to 0.75 inches, and most preferably about 0.3 to 0.5 inches. In this embodiment, the shell layer has a surface hardness that is greater than its inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient.

The thermoplastic outer core layer has a second hardness gradient. The shell layer has a surface hardness greater than about 55 Shore C. The shell layer has a coefficient of restitution (COR) less than about 0.750 when measured at an incoming velocity of 125 ft/s. Preferably, the COR is less than about 0.700, more preferably about 0.500 to 0.700, and most preferably about 0.600 to 0.700. The overall core (the combination of the hollow core and any outer core layers) has a COR, measured at an incoming velocity of 125 ft/s, higher than the COR of the shell layer by greater than about 5%, more preferably about 10 to 50%, and most preferably about 15 to 30%.

In an alternative embodiment, the hardness gradient of the thermoplastic outer core layer has a ‘zero hardness gradient’. The zero hardness gradient is typically about 0 Shore C (defined herein as ±2 Shore C). The hardness gradient of the thermoplastic outer core layer may also have a ‘negative hardness gradient’, preferably about 1 to 10 Shore C, more preferably about 2 to 8 Shore C, and most preferably about 2 to 5 Shore C. The hardness gradient of the thermoplastic outer core layer may also have a ‘positive hardness gradient’, preferably about 1 to 10 Shore C, more preferably about 2 to 8 Shore C, and most preferably about 2 to 5 Shore C.

The golf ball has a first volume and the plurality of extensions and innermost aspherical hollow portion, combined, has a second volume. The second volume is about 2% to 30% of the first volume, more preferably about 5% to 25% of the first volume, and most preferably about 10% to 20% of the golf ball volume.

The hollow core of the present invention (innermost aspherical hollow portion, shell layer and outer core layer(s)) is covered by at least one cover layer. An intermediate layer, such as an inner cover layer, may optionally be disposed about the hollow core, with the cover layer formed around the intermediate layer as an outer cover layer. While any of the thermoplastic materials disclosed herein may be suitable for the inner or outer cover layers of the invention, in one embodiment the outermost cover is formed from a castable polyurea or a castable polyurethane; castable hybrid poly(urethane/urea); and castable hybrid poly(urea/urethane). Suitable polyurethanes include those disclosed in U.S. Pat. Nos. 5,334,673 and 6,506,851. Suitable polyureas include those disclosed in U.S. Pat. Nos. 5,484,870 and 6,835,794. These patents are incorporated herein by reference thereto.

Other suitable polyurethane compositions comprise a reaction product of at least one polyisocyanate and at least one curing agent. The curing agent can include, for example, one or more polyamines, one or more polyols, or a combination thereof. The polyisocyanate can be combined with one or more polyols to form a prepolymer, which is then combined with the at least one curing agent. Thus, the polyols described herein are suitable for use in one or both components of the polyurethane material, i.e., as part of a prepolymer and in the curing agent. More suitable polyurethanes are described in U.S. Pat. No. 7,331,878, which is incorporated by reference in its entirety.

Any polyisocyanate available to one of ordinary skill in the art is suitable for use according to the invention. Exemplary polyisocyanates include, but are not limited to, 4,4′-diphenylmethane diisocyanate (MDI); polymeric MDI; carbodiimide-modified liquid MDI; 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI); p-phenylene diisocyanate (PPDI); m-phenylene diisocyanate (MPDI); toluene diisocyanate (TDI); 3,3′-dimethyl-4,4′-biphenylene diisocyanate; isophoronediisocyanate; 1,6-hexamethylene diisocyanate (HDI); naphthalene diisocyanate; xylene diisocyanate; p-tetramethylxylene diisocyanate; m-tetramethylxylene diisocyanate; ethylene diisocyanate; propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; cyclohexyl diisocyanate; dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methyl cyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of 2,4,4-trimethyl-1,6-hexane diisocyanate; tetracene diisocyanate; napthalene diisocyanate; anthracene diisocyanate; isocyanurate of toluene diisocyanate; uretdione of hexamethylene diisocyanate; and mixtures thereof. Polyisocyanates are known to those of ordinary skill in the art as having more than one isocyanate group, e.g., di-isocyanate, triisocyanate, and tetra-isocyanate. Preferably, the polyisocyanate includes MDI, PPDI, TDI, or a mixture thereof, and more preferably, the polyisocyanate includes MDI. It should be understood that, as used herein, the term MDI includes 4,4′-diphenylmethane diisocyanate, polymeric MDI, carbodiimide-modified liquid MDI, and mixtures thereof and, additionally, that the diisocyanate employed may be “low free monomer,” understood by one of ordinary skill in the art to have lower levels of “free” monomer isocyanate groups, typically less than about 0.1% free monomer isocyanate groups. Examples of “low free monomer” diisocyanates include, but are not limited to Low Free Monomer MDI, Low Free Monomer TDI, and Low Free Monomer PPDI. The at least one polyisocyanate should have less than about 14% unreacted NCO groups. Preferably, the at least one polyisocyanate has no greater than about 8.0% NCO, more preferably no greater than about 7.8%, and most preferably no greater than about 7.5% NCO with a level of NCO of about 7.2 or 7.0, or 6.5% NCO commonly used.

Any polyol available to one of ordinary skill in the art is suitable for use according to the invention. Exemplary polyols include, but are not limited to, polyether polyols, hydroxy-terminated polybutadiene (including partially/fully hydrogenated derivatives), polyester polyols, polycaprolactone polyols, and polycarbonate polyols. In one embodiment, the polyol includes polyether polyol. Examples include, but are not limited to, polytetramethylene ether glycol (PTMEG), polyethylene propylene glycol, polyoxypropylene glycol, and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds and substituted or unsubstituted aromatic and cyclic groups. Preferably, the polyol of the present invention includes PTMEG.

In another embodiment, polyester polyols are included in the polyurethane material. Suitable polyester polyols include, but are not limited to, polyethylene adipate glycol; polybutylene adipate glycol; polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol; poly(hexamethylene adipate)glycol; and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in the materials of the invention. Suitable polycaprolactone polyols include, but are not limited to, 1,6-hexanediol-initiated polycaprolactone, diethylene glycol initiated polycaprolactone, trimethylol propane initiated polycaprolactone, neopentyl glycol initiated polycaprolactone, 1,4-butanediol-initiated polycaprolactone, and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, polycarbonate polyols are included in the polyurethane material of the invention. Suitable polycarbonates include, but are not limited to, polyphthalate carbonate and poly(hexamethylene carbonate)glycol. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups. In one embodiment, the molecular weight of the polyol is from about 200 to about 4000.

Polyamine curatives are also suitable for use in the polyurethane composition of the invention and have been found to improve cut, shear, and impact resistance of the resultant balls. Preferred polyamine curatives include, but are not limited to, 3,5-dimethylthio-2,4-toluenediamine and isomers thereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof, such as 3,5-diethyltoluene-2,6-diamine; 4,4′-bis-(sec-butylamino)-diphenylmethane; 1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline); 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline; m-phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline); 4,4′-methylene-bis-(2,6-diethylaniline); 4,4′-methylene-bis-(2,3-dichloroaniline); 4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane; 2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycol di-p-aminobenzoate; and mixtures thereof. Preferably, the curing agent of the present invention includes 3,5-dimethylthio-2,4-toluenediamine and isomers thereof, such as ETHACURE® 300, commercially available from Albermarle Corporation of Baton Rouge, La. Suitable polyamine curatives, which include both primary and secondary amines, preferably have molecular weights ranging from about 64 to about 2000.

At least one of a diol, triol, tetraol, or hydroxy-terminated curatives may be added to the aforementioned polyurethane composition. Suitable diol, triol, and tetraol groups include ethylene glycol; diethylene glycol; polyethylene glycol; propylene glycol; polypropylene glycol; lower molecular weight polytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene; 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl) ether; hydroquinone-di-(β-hydroxyethyl) ether; and mixtures thereof. Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy)benzene; 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol, and mixtures thereof. Preferably, the hydroxy-terminated curatives have molecular weights ranging from about 48 to 2000. It should be understood that molecular weight, as used herein, is the absolute weight average molecular weight and would be understood as such by one of ordinary skill in the art.

Both the hydroxy-terminated and amine curatives can include one or more saturated, unsaturated, aromatic, and cyclic groups. Additionally, the hydroxy-terminated and amine curatives can include one or more halogen groups. The polyurethane composition can be formed with a blend or mixture of curing agents. If desired, however, the polyurethane composition may be formed with a single curing agent.

In one embodiment of the present invention, saturated polyurethanes are used to form one or more of the cover layers, preferably the outer cover layer, and may be selected from both castable thermoset and thermoplastic polyurethanes. In this embodiment, the saturated polyurethanes of the present invention are substantially free of aromatic groups or moieties. Saturated polyurethanes suitable for use in the invention are a product of a reaction between at least one polyurethane prepolymer and at least one saturated curing agent. The polyurethane prepolymer is a product formed by a reaction between at least one saturated polyol and at least one saturated diisocyanate. As is well known in the art, that a catalyst may be employed to promote the reaction between the curing agent and the isocyanate and polyol, or the curing agent and the prepolymer.

Additionally, polyurethane can be replaced with or blended with a polyurea material. Polyureas are distinctly different from polyurethane compositions. The polyurea-based compositions are preferably saturated in nature. The polyurea compositions may be formed from the reaction product of an isocyanate and polyamine prepolymer crosslinked with a curing agent. For example, polyurea-based compositions of the invention may be prepared from at least one isocyanate, at least one polyether amine, and at least one diol curing agent or at least one diamine curing agent.

Golf balls of the invention and any thermoplastic or thermoset layer disclosed herein may be formed using a variety of application techniques such as compression molding, flip molding, injection molding, retractable pin injection molding, reaction injection molding (RIM), liquid injection molding (LIM), casting, vacuum forming, powder coating, flow coating, spin coating, dipping, spraying, and the like. Conventionally, compression molding and injection molding are applied to thermoplastic materials, whereas RIM, liquid injection molding, and casting are employed on thermoset materials. These and other manufacture methods are disclosed in U.S. Pat. Nos. 6,207,784 and 5,484,870, the disclosures of which are incorporated herein by reference in their entirety.

For example, intermediate or cover layers may be formed using any suitable method known to those of ordinary skill in the art such as by blow molding an intermediate layer and covering with a dimpled cover layer formed by injection molding, compression molding, casting, vacuum forming, powder coating, and the like. A composition may be dry-blended and fed into an injection molding machine to produce half cups, or may be formed by melt blending and extruding the components with polymer mixing equipment, such as a single or twin-screw extruder. Pellets may be dry blended with other components and then injection molded onto any inner layer. Compression molding or retractable pin injection molding may be used to seal cups together and form a finished golf ball.

A method of injection molding using a split vent pin can be found in co-pending U.S. Pat. No. 6,877,974, filed Dec. 22, 2000, entitled “Split Vent Pin for Injection Molding.” Examples of retractable pin injection molding may be found in U.S. Pat. Nos. 6,129,881; 6,235,230; and 6,379,138. These molding references are incorporated in their entirety by reference herein. In addition, a chilled chamber, i.e., a cooling jacket, such as the one disclosed in U.S. Pat. No. 6,936,205, filed Nov. 22, 2000, entitled “Method of Making Golf Balls” may be used to cool the compositions of the invention when casting, which also allows for a higher loading of catalyst into the system.

Conventionally, compression molding and injection molding are applied to thermoplastic materials, whereas RIM, liquid injection molding, and casting are employed on thermoset materials. These and other manufacture methods are disclosed in U.S. Pat. Nos. 6,207,784 and 5,484,870, the disclosures of which are incorporated herein by reference in their entirety.

Castable reactive liquid polyurethanes and polyurea materials may be applied over the inner ball using a variety of application techniques such as casting, injection molding spraying, compression molding, dipping, spin coating, or flow coating methods that are well known in the art. In one embodiment, the castable reactive polyurethanes and polyurea material is formed over the core using a combination of casting and compression molding. Conventionally, compression molding and injection molding are applied to thermoplastic cover materials, whereas RIM, liquid injection molding, and casting are employed on thermoset cover materials.

U.S. Pat. No. 5,733,428, the entire disclosure of which is hereby incorporated by reference, discloses a method for forming a polyurethane cover on a golf ball core. Because this method relates to the use of both casting thermosetting and thermoplastic material as the golf ball cover, wherein the cover is formed around the core by mixing and introducing the material in mold halves, the polyurea compositions may also be used employing the same casting process.

For example, once a polyurea composition is mixed, an exothermic reaction commences and continues until the material is solidified around the core. It is important that the viscosity be measured over time, so that the subsequent steps of filling each mold half, introducing the core into one half and closing the mold can be properly timed for accomplishing centering of the core cover halves fusion and achieving overall uniformity. A suitable viscosity range of the curing urea mix for introducing cores into the mold halves is determined to be approximately between about 2,000 cP and about 30,000 cP, or within a range of about 8,000 cP to about 15,000 cP.

To start the cover formation, mixing of the prepolymer and curative is accomplished in a motorized mixer inside a mixing head by feeding through lines metered amounts of curative and prepolymer. Top preheated mold halves are filled and placed in fixture units using centering pins moving into apertures in each mold. At a later time, the cavity of a bottom mold half, or the cavities of a series of bottom mold halves, is filled with similar mixture amounts as used for the top mold halves. After the reacting materials have resided in top mold halves for about 40 to about 100 seconds, preferably for about 70 to about 80 seconds, a core is lowered at a controlled speed into the gelling reacting mixture.

A ball cup holds the shell through reduced pressure (or partial vacuum). Upon location of the core in the halves of the mold after gelling for about 4 to about 12 seconds, the vacuum is released allowing the core to be released. In one embodiment, the vacuum is released allowing the core to be released after about 5 seconds to 10 seconds. The mold halves, with core and solidified cover half thereon, are removed from the centering fixture unit, inverted and mated with second mold halves which, at an appropriate time earlier, have had a selected quantity of reacting polyurea prepolymer and curing agent introduced therein to commence gelling.

Similarly, U.S. Pat. No. 5,006,297 and U.S. Pat. No. 5,334,673 both also disclose suitable molding techniques that may be utilized to apply the castable reactive liquids employed in the present invention.

However, golf balls of the invention may be made by any known technique to those skilled in the art.

While any of the embodiments herein may have any known dimple number and pattern, a the number of dimples may be 252 to 456, or 330 to 392, for example. The dimples may comprise any width, depth, and edge angle disclosed in the prior art and the patterns may comprises multitudes of dimples having different widths, depths and edge angles. The parting line configuration of said pattern may be either a straight line or a staggered wave parting line (SWPL). Most preferably the dimple number is 330, 332, or 392 and comprises 5 to 7 dimples sizes and the parting line is a SWPL.

In any of these embodiments the single-layer core may be replaced with a 2 or more layer core wherein at least one core layer has a negative hardness gradient. Other than in the operating examples, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials and others in the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used.

While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objective stated above, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which would come within the spirit and scope of the present invention. 

What is claimed is:
 1. A golf ball comprising: a hollow core comprising: an innermost spherical hollow portion having a diameter of about 0.15 inches to about 1.1 inches; surrounded by a shell layer formed from a thermoplastic composition; and at least one outer core layer formed from a thermoset composition disposed about the shell layer; wherein the shell layer has a non-uniform thickness, an inner surface having an inner surface hardness, and an outer surface having an outer surface hardness greater than the inner surface hardness by up to about 7 Shore C to define a first hardness gradient; and an outer core layer formed about the outer surface and having a second hardness gradient; and at least one cover layer disposed about the core.
 2. The golf ball of claim 1, wherein the inner surface has a non-uniform contour that defines a phantom spherical circumference of the innermost spherical hollow portion at symmetrically spaced locations about a geometric center of the golf ball.
 3. The golf ball of claim 1, wherein the outer surface has a non-uniform contour that borders and defines a contour of a second inner surface of the outer core layer, wherein the outer surface hardness and a second inner surface hardness of the second inner surface differ.
 4. The golf ball of claim 1, wherein the first hardness gradient is about 1 to 5 Shore C.
 5. The golf ball of claim 1, wherein the second hardness gradient is a negative hardness gradient of about 3 to 25 Shore C.
 6. The golf ball of claim 1, wherein the second hardness gradient is a positive hardness gradient of about 3 to 25 Shore C.
 7. The golf ball of claim 1, wherein the cover comprises an inner cover layer disposed about the outer core layer and comprising an ionomeric material and having a first hardness; and an outer cover layer disposed about the inner cover layer and comprising a polyurea or a polyurethane and having a second hardness less than the first.
 8. A golf ball comprising: a core comprising: an innermost aspherical hollow portion having a volume V_(ahp); surrounded by a shell layer that is formed from a thermoplastic composition and has an inner surface comprising a plurality of symmetrically spaced extensions that border and define a shape of the innermost aspherical hollow portion; wherein the plurality of extensions and innermost aspherical hollow portion, combined, form a phantom sphere having a diameter of from about 0.15 inches to about 1.1 inches; and wherein the plurality of extensions have a combined total volume E_(TV) such that V_(ahp)≧E_(TV)>0.20 (E_(TV)+V_(ahp)); and wherein an outer surface of the shell layer has a non-uniform contour and an outer surface hardness greater than an inner surface hardness of the inner surface by up to about 7 Shore C to define a first hardness gradient; and an outer core layer disposed about the outer surface and having a second hardness gradient; and at least one cover layer disposed about the outer core layer.
 9. The golf ball of claim 8, wherein the aspherical hollow portion has a shape that is axially symmetric.
 10. The golf ball of claim 9, wherein the aspherical hollow portion is at least one of non-spherical or irregularly-shaped.
 11. The golf ball of claim 8, wherein the plurality of extensions and innermost aspherical hollow portion, combined, form a spherical phantom sphere having a diameter of from about 0.30 inches to about 0.90 inches.
 12. The golf ball of claim 8, wherein the non-uniform contour borders and defines a contour of a second inner surface of the outer core layer, wherein the outer surface hardness and a second inner surface hardness of the second inner surface differ.
 13. The golf ball of claim 8, wherein the first hardness gradient is about 1 to 5 Shore C.
 14. The golf ball of claim 8, wherein the at least one cover layer comprises an inner cover layer disposed about the outer core layer and comprising an ionomeric material and having a first hardness; and an outer cover layer disposed about the inner cover layer and comprising a polyurea or a polyurethane and having a second hardness less than the first.
 15. The golf ball of claim 8, wherein the innermost aspherical hollow portion, shell layer and outer core layer, combined, have an outer diameter of from about 0.75 inches to about 1.62 inches.
 16. The golf ball of claim 8, wherein the second hardness gradient is a negative hardness gradient of about 3 to 25 Shore C.
 17. The golf ball of claim 8, wherein the second hardness gradient is a positive hardness gradient of about 3 to 25 Shore C.
 18. The golf ball of claim 8, wherein the outer core layer is formed from a thermoset composition.
 19. The golf ball of claim 8, wherein at least one outer core layer is formed from a thermoplastic composition.
 20. A golf ball comprising: a core comprising: a shell layer that is formed from a thermoplastic composition and has an inner surface comprising a plurality of symmetrically spaced extensions that border and define a shape of an innermost aspherical hollow portion; wherein the innermost aspherical hollow portion comprise from about 2% to about 30% of a total volume of the golf ball; wherein an outer surface of the shell layer has a non-uniform contour and an outer surface hardness greater than an inner surface hardness of the inner surface by up to about 7 Shore C to define a first hardness gradient; and an outer core layer disposed about the outer surface and having a second hardness gradient; and at least one cover layer disposed about the core.
 21. The golf ball of claim 20, wherein the innermost aspherical hollow portion has a shape that is axially symmetric.
 22. The golf ball of claim 21, wherein the innermost aspherical hollow portion is at least one of non-spherical or irregularly-shaped.
 23. The golf ball of claim 20, wherein the plurality of extensions and innermost aspherical hollow portion, combined, form a phantom sphere having a diameter of from about 0.15 inches to about 1.1 inches.
 24. The golf ball of claim 20, wherein the non-uniform contour borders and defines a contour of a second inner surface of the outer core layer, wherein the outer surface hardness and a second inner surface hardness of the second inner surface differ.
 25. The golf ball of claim 20, wherein the first hardness gradient is about 1 to 5 Shore C.
 26. The golf ball of claim 20, wherein the at least one cover layer comprises an inner cover layer disposed about the outer core layer, and an outer cover layer disposed about the inner cover layer, wherein the inner cover layer comprises an ionomeric material and has a first hardness, and the outer cover layer comprises a polyurea or a polyurethane and has a second hardness less than the first.
 27. The golf ball of claim 20, wherein the innermost aspherical hollow portion, shell layer and outer core layer, combined, have an outer diameter of from about 0.75 inches to about 1.62 inches.
 28. The golf ball of claim 20, wherein the second hardness gradient is a negative hardness gradient of about 3 to 25 Shore C.
 29. The golf ball of claim 20, wherein the second hardness gradient is a positive hardness gradient of about 3 to 25 Shore C.
 30. The golf ball of claim 20, wherein at least one outer core layer is formed from a thermoset composition.
 31. The golf ball of claim 20, wherein at least one outer core layer is formed from a thermoplastic composition. 